PCV modes like BIPAP are safe in ARDS patient as long the alarm of the minimal tidal volume is set to a safe limit. Otherwise by decreased compliance of the lung the patient is ventilated with a much lesser tidal volume. Consequence could be a increase of CO² and respiratory acidosis causing cardio-circulatory depression or renal failure. The recommended tidal volume(ARDS-Network) is around 6ml/kg Ideal body weight. So I start with volume controled ventilation setting the tidal volumen to the recommended value (e.g. 6x80Kg=480ml). Then I watch the pressures generated by this mode (e.g. PEEP 10 Pmax 26mbar) followed by a switch to BIPAP with 10/26 values. Alarmlimits should be set to tidal volume min 450ml max 550ml or a minute volume alarm (with breath frequence 12/min) min.5,4l/min max. 6,6l/min. In addition if available you could use a continuous CO²-Monitoring. Its is like in every maschine/computer: It is as safe or clever as the user using it.

One advantage of VCV is the easy control of volume and thus to ensure the so-called small tidal ventilation; so long as the pressure limit is properly set, the safety of patients can be secured. In the landmark study by amato in NEJM, they used volume control mode( I am not very sure here).

First, I do not believe the mode of ventilation makes a significant impact on mortality provided low tidal volume/pressures are maintained. That said, i believe that in most ventilators I have used, the pressure control mode allows for greater flow variability and can improve patient ventilator synchrony with lower sedation requirements in selected cases. As long as the appropriate alarms are in place I do not worry about moderate elevations in carbon dioxide, I am much more concerned about elevation in airway pressures. Certainly the ARDS trial suggests that alveolar distending pressure is more closely related to mortality than hypercarbia.

Ventilation management in ARDS rests on achieving adequate oxygenation while limiting lung injury. Tharratt and colleagues were able to show (Chest 1988; 94:755) that PC-IRV achieved significant improvement in oxygenation at lower minute volumes, peak airway pressures and PEEP requirements. These findings were confirmed by Rappaport et al (CCM 1994; 22:22) using pressure-limited ventilation. Although to my knowledge no mortality benefit has been demonstrated, pressure control is safe, and in my experience, makes it clinically easier to achieve the goals. Anecdotally, I've noted that early application of PC-IRV reduces the failure rate, and thus reduces the need to proceed to ECMO or oscillatory modes (although I like HFO as rescue therapy when PC-IRV isn't enough).

I tend to agree with Dr. Higgins. I find it useful to use PCV maybe even with relatively greater I:E ratios ( like 1:1) when on ACV low TV are still resulting in high plateau pressures. This will sometimes let you achieve low plateaus but not have to drop the TV to really low levels like 4-5, and helps keep gas exchange at reasonable levels. Many patients also find PCV more comfortable because they like the better flow rates.

In my humble opinion using modes which assure a tidal volume require less changes, so I cannot understand the advantage using PC instead of PRVC or Autoflow.

ARDS patients have a short time constant, so high respiratory rate and short inspiratory time are easily obtained will all the modes. As far as I know, goals are achieved earlier with volume control rather than pressure control ( there is a randomized trial in neonates that proved that; Arch Diseases Child Neonatal 1997

Regarding to I.E ratios, it has been demonstrated that it works because you are generating inadvertent PEEP....so I prefer to increase the PEEP rather than modify I:E ratios.

A question for Dr Cardenas: How can you improve the synchrony in a pressure mode compared with a volume mode if both have the same inspiratory trigger? I am sorry, I can not understand!

As mentioned, the strategy of ventilation should focus on improving oxygenation and prevention of complication with the using of the well described ventilatory sittings and variables. I find it useful to use dual modes like ( Pressure Regulated Volume Control )(PRVC) so, with that you guarantee suitable volume and pressure at the same time.

I use VC, PC or BiLevel. In the sickest ARDS patients I find BiLevel is generally the mode which results in the least dysynchrony while achieving standard ARDS pressure and volume goals. However the volumes need close monitoring as compliance changes. Of course BiLevel s a waste of time if you are following the French and paralysing for the first 48 hours.

PCV is good in particular when the desired volume cannot be delivered. It buys time and prevents barotrauma.

PCV is safer in ARDS. It delivers the volume required to set the pressure limit and the rest is released out. It is a safety strategy and may be, slowly allow the baby lung to recover. I change from IMV to PCV if I don’t achieve the PO2 I want or think appropriate for the clinical status. It has helped in some patients to reverse the clinical scenario.

Pressure control ventilation alone is harmful during ARDS.

The main problem during ARDS mechanical ventilation (MV) is to avoid ventilator lung injury ( VLI) by overdistension due to baro or volotraumas.

In the 80’s, before the implementation of the new concept of lung –protective MV strategies with secondary permissive hypercapnia, we used as all the high tidal volume to reach or to try to obtain a PCO2 near to 45 mmhg. At evidence, this approach was catastrophic in term of pneumothorax due to alveoli overdistension and survival.

In the 1990’s, before the results of the pivotal studies, within the consensus conference and the new knowledge that ARDS per se may induce multiorgan failure, we used two strategies to avoid VLI, the static pressure/volume curves being not available in the current ventilators: a VT of 8ml/kg or pressure controlled ventilation with a plateau pressure of 30 cm H2O. This strategy was very rapidly abandoned in view of immediate overdistension with potential volotrauma in majority of ARDS. Furthermore, we observed that the low tidal strategy was more evident for all the staff and safe if the tidal volume is progressively decreased. I remember the major hemodynamic consequences and the acute respiratory failure ( PH < 7) when a young fellow switch the tidal volume from 13 ml/kg to 7 ml/kg.

Now, we use systematically the ARDS network and VT recommendations, but we must frequently control that VT is adjusted to the predicted body weight.

Thus, if the concept of controlled pressure MV is of interest, I believe that it may be harmful if the plateau pressure is not adjusted to the compliance. Volume control ventilation should be the gold standard.

Ι will agree with Anthony. PCV needs continuous attendance of an experienced person, but can save lives and lungs. It must be continuously reassessed and changed to VCV if needed.

Volume control ventilation (VCV) is not exactly the “gold standard” for ARDS patients. But, according to the Surviving Sepsis Campaign recently updated with international guidelines for sepsis, experts target a tidal volume ( VT) of 6ml/Kg of Predicted body weight and an upper limit goal for plateau pressure measured in a passively inflated lung < 30cm H2O (Intensive Care Medecine 2013). Thus, I believe that this guideline should the key message for our fellows. Using EBM, we could argue that all the pivotal studies were performed with VCV and that, to date, no randomized controlled trial have compared VCV to Pressure controlled ventilation (PCV).

On the ongoing debate, PCV users might argue that with PCV square wave, plateau pressure can never be greater than the peak inspiratory pressure, may improve ventilation/perfusion matching and PaO2. Others may evocate the potential risk with the initial high flow rate.

PCV has been used as a ventilation rescue in some case reports, but I am not so sure that similar results could not be obtained with VCV optimization.

I agree completely with the fact that a PCV expert can perform safely a lung protective ventilation based on limitation of Vt and alveolar distending pressure, but for clinical practice and safety, I recommend to follow the standard guidelines.

Dear all

Regrading the appropriate mode of MV in ARDS, Currently available data from RCTs are insufficient to confirm or refute whether pressure-controlled or volume-controlled ventilation offers any advantage for people with acute respiratory failure due to acute lung injury or acute respiratory distress syndrome. More studies including a larger number of people given PCV and VCV may provide reliable evidence on which more firm conclusions can be based. (Cochrane Database Syst Rev. 2015)

Most of the publications done in VC mode, it does not translate to VC better than PC mode. It is our common practice in our PICU to use PC mode or HFOV in severe ARDS.

Best

Rujipat

Ped Intensivist

Bkk, Thailand